非绝热分子动力学模拟A位阳离子对钙钛矿热载流子弛豫的影响

钙钛矿具有优异的光学和电学性质,近年来成为太阳能电池领域的研究热点.大量实验报道钙钛矿热载流子弛豫时间变化顺序为CsPbBr₃>MAPbBr₃(MA=CH₃NH₃)>FAPbBr₃[FA=HC(NH₂)₂],但A位阳离子(Cs⁺,MA⁺,FA⁺)对弛豫快慢的影响机制仍不明确.采用基于含时密度泛函理论的非绝热动力学方法研究了上述3种钙钛矿热电子和热空穴的能量弛豫动力学,计算得到的热载流子弛豫时间与实验结果吻合.结果表明,A位阳离子通过静电和氢键作用影响其与无机Pb—Br骨架的电子-振动耦合,使非绝热耦合强度遵从FAPbBr₃>MAPbBr₃>CsPbBr₃的变化趋势,进而使热载流子弛豫时间尺度变化趋势与之相同,表明合理选择A位阳离子可以优化钙钛矿太阳能电池的性能.

A-site Cation Effects on Hot Carrier Relaxation in Perovskites by Nonadiabatic Molecular Dynamics Simulations †

In recent years, perovskites have become a research hotspot in the field of solar cells due to their excellent optical and electrical properties. A large number of experiments reported that hot carries relaxation times follow the trend CsPbBr₃>MAPbBr₃(MA=CH₃NH₃)>FAPbBr₃[FA=HC(NH₂)₂]. However, the underlying mechanism of the A-site cation(Cs ⁺, MA ⁺, FA ⁺) effects on the relaxation time remains unclear, the hot electrons and holes relaxation of the three perovskiteswere investigated using time-domain density functional theory combined with nonadiabatic molecular dynamics. The obtained time scales agreed well with experiment. This is because A-site cation affects electronic-vibrational coupling with the inorganic Pb—Br framework via electrostatic interaction and hydrogen bond, leading to the strength of nonadiabatic coupling decreasing from FAPbBr₃ to MAPbBr₃, to CsPbBr₃. As a result, the hot carrier relaxation times decreases as the same trend. The study suggests that rational choice of A-site cations provides an excellent strategy to the optimize the performance of perovskite solar cells.